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Introduction to Remote Sensing Lecture 1

Introduction to Remote Sensing Lecture 1. Summer Session 12 July 2011. Basic Info. Lecturer: Alyssa Whitcraft alyssakw@gmail.com Office Hours: by appointment TA: Sumalika Biswas Sumalika.biswas@gmail.com Office Hours: 4-6 pm, Tuesday/Thursday – ONLINE Grading Breakdown:.

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Introduction to Remote Sensing Lecture 1

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  1. Introduction to Remote Sensing Lecture 1 Summer Session12 July 2011

  2. Basic Info • Lecturer: Alyssa Whitcraft • alyssakw@gmail.com • Office Hours: by appointment • TA: SumalikaBiswas • Sumalika.biswas@gmail.com • Office Hours: 4-6 pm, Tuesday/Thursday – ONLINE • Grading Breakdown:

  3. Questions About You • Introductions: • Name? • Major(s)/Minor(s)? • Why are you taking this class? • For many it is a requirement – but anything else? • Any background relative to remote sensing? • PLEASE POST TO THE DISCUSSION BOARD BY THURSDAY 14 JULY 2011

  4. Today’s Topics • Introduction to Online Interface - Questions • Remote Sensing: What? and Why? • Basics of Electromagentic (EM) Radiation • Wave & Particle Theory • Radiation Laws and Theories • Lab 1 – Data Sources

  5. You will see the slides here! Click to talk, or hold down “ctrl” or “F8” Click to activate video camera Who is in the room, and what their status & capabilities are Chat Box Change your “status” Yes or No (respond to questions) Raise your hand

  6. A note about labs • You do not have to “attend” online labs • There are not enough Citrix licenses for everyone in the department of Geography to be online at once, unfortunately. • Sumalika will be available for 8 hours a week • Tuesday/Thursday 4-6 pm and 7:30-9:30 pm • We may have to split groups into two and only allow access for half of the class at a time if it becomes an issue. • Sumalika will review labs after lecture (~7:30 pm) so people are prepared to complete them on their own time • If some students are repeatedly unable to login, then we (instructors) will have to take action • Other options: • Open lab: Monday-Friday, ~10 am – 4 pm (LEF 1136/8)

  7. What is Remote Sensing? • Remote sensing uses the radiant energy that is reflected, emitted, or scattered from the Earth and its atmosphere from various portions (“wavelengths”) of the electromagnetic (EM) spectrum • Our eyes are only sensitive to the “visible light” portion of the EM spectrum – but there is MUCH more that remote sensing makes available/useful to us!

  8. Why Remote Sensing? • Electromagnetic energy being detected by remote sensors is dependent on the characteristic of the surface or atmosphere being sensed – • Remote sensing provides unique information • Many portions of the earth’s surface and atmosphere are difficult to sample and measure using in situ measurements • Only way to systematically collect data in many regions • Remote sensors can continuously collect data • Reliable and consistent source of information

  9. Definitions of remote sensing Our basic definition Definition 1 –Remote sensing is the acquiring of information about an object or scene without touching it through using electromagnetic energy. Issues? - we limit ourselves to electromagnetic energy, yet many systems use sound waves to acquire data. - includes smell, etc.

  10. Elements of a Remote Sensing System 4. Data Recorder 3. Sensing Device 5. Information Production System 6. Information Delivery System 2. Area or scene of interest 1. Information User

  11. Basic Remote Sensing System – Aerial Photography Sun Camera System - Used photographic film, paper products, and simple cartographic representations (we’ll learn more about this in Lecture 3).

  12. Definitions of remote sensing Definition 2 –Remote sensing is the non-contact recording of information from the UV, visible, IR, and microwave regions of the EM spectrum by means of a variety of electro-optical systems, and the generation and delivery of information products based on the processing of these data

  13. Categories of Remote Sensors Remote sensors are based on: • Specific regions of the EM spectrum • The types of EM energy being detected • The source of EM energy, e.g., passive versus active sensors

  14. Ultraviolet (  < 0.4 m) Visible ( 0.4 m <  < 0.7 m) Reflected IR ( 0.7 m <  < 2.8 m) Emitted (thermal) IR ( 2.4 m <  < 20 m) Microwave ( 1 cm <  < 1 m) EM Spectrum Regions Used in Remote Sensing  = EM radiation wavelength VERY IMPORTANT!!

  15. Thermal IR Sensors • Thermal IR deals with the Far IR region of the EM spectrum, wavelengths between 2.4 and 20 µm • Most Thermal IR scanners use wavelengths between 8 and 15 µm

  16. Microwave remote sensing instruments operate at wavelengths greater than 1 mm • Figure 1-18 from Elachi, C., Introduction to the Physics and Techniques of Remote Sensing, 413 pp., John Wiley & Sons, New York, 1987.

  17. Categories of Remote Sensors Remote sensors are based on • Specific regions of the EM spectrum • The types of EM energy being detected • The source of EM energy, e.g., passive versus active sensors

  18. Types of EM energy detected by remote sensors 3. Scattered EM energy Atmosphere 1. Reflected energy 2. Emitted EM energy 1. Reflected EM energy Earth surface

  19. Passive vs. active systems • Passive systems record energy that is emitted, scattered or reflected from natural sources (e.g., sunlight or based on the temperature of the surface or atmosphere being imaged) • Active systems provide their own source of EM radiation, which is then reflected or scattered, and this signal detected by the system

  20. 6000º K emitted UV, Visible, Near IR Sensors Active Sensors Microwave, Visible scattered Thermal IR, Microwave Sensors reflected emitted 300º K emitted

  21. Definition of resolution • Also referred to as resolving power • Defined as the ability of a remote sensor to distinguish between signals that are similar • Four types of resolution important in remote sensing – • Spatial • Spectral • Radiometric • Temporal  KNOW THESE!

  22. Spatial Resolution • The measure of the smallest distance (linear or angular separation) between objects that can be resolved by the sensor. • e.g. Landsat 7  15-60 m resolution • e.g. MODIS  250-1000 m resolution Figure 1-8 from Jensen

  23. Spectral Resolution • Refers to the dimensions (widths) and wavelength regions of the EM spectrum a specific sensor is sensitive to

  24. Spectral Bands in a Visible and Near IR Remote Sensor Sensor has 6 different bands or channels Each band has a center wavelength Each band has a width

  25. Spectral Resolution • Most remote sensing systems collect data in 1 to 10 different wavelength regions or bands, each with broad width • e.g. Landsat 7  7 visible/IR bands (including 1 thermal), and 1 panchromatic band • e.g. MODIS  36 visible/IR bands • Hyperspectral remote sensing systems have a large number of very narrow bands]

  26. Radiometric Resolution • The sensitivity of a remote sensing detector to variations in the intensity of the emitted, reflected or scattered EM energy that is being detected • theprecision of the system • e.g. Landsat 7  8-bit system • e.g. MODIS  12-bit system

  27. Radiometric Resolution How many different intensity levels can be discriminated by the remote sensor within a specific band?

  28. Temporal Resolution • How often a remote sensor has the ability to record data over the same area • e.g. Landsat 7  16 days • e.g. MODIS  Daily

  29. Examples of Remote Sensing Information Products • Global land cover • Global agricultural monitoring information – cropped area and crop production forecasts • Active fire locations • Ocean chlorophyll • Flooding patterns in the Florida Everglades • Gulf Stream flow • El Nino sea surface temperature • Global wind patterns • Atmospheric trace gas/aerosol concentrations • The Antarctic Ozone Hole • Breakup of the Larsen Ice Sheet • Arctic sea ice cover

  30. The Basics of EM Radiation

  31. Basic Energy Principles • Energy is the ability to do work • There are three ways to transfer energy from one place or object to another • Conduction • Convection • Radiation – energy emitted into space by any object above 0 degrees K

  32. Conduction – transfer of energy through collisions of atoms or molecules

  33. Convection - physically moving the molecules/atoms from one place to another

  34. Radiation – energy emitted into space by any object above 0° K

  35. Models of EM Radiation • Wave Model of EM Energy – describes how EM radiation is propagated, e.g., how it moves through space • Particle Model of EM Energy – describes how EM radiation interacts with matter

  36. The Electromagnetic Wave • EM energy travels with the speed of light, c, • Within a vacuum c = 3 x 108 m sec-1

  37. The Electromagnetic Wave EM energy consists of two fluctuating fields perpendicular to each other and both perpendicular to the direction of energy movement • An electrical field • A magnetic field

  38. Polarization • Polarization refers to the relative orientation of the electrical field of an EM wave • Horizontal polarization - an EM wave that is parallel to the earth’s surface • Vertical polarization - an EM wave that is perpendicular to the earth’s surface  an important consideration in microwave remote sensing

  39. Radar systems control the polarization of both the transmitted and received microwave EM energy Figure 9.6 from Jensen

  40. Characteristics of EM radiation • Created whenever an electrical charge is accelerated • Two characteristics of EM waves Wavelength () – depends on the length of time over which the electrical charge is accelerated Frequency () depends on the number of accelerations per second

  41. EM Frequency () • Frequency is expressed in hertz, where one hertz is one cycle or wavelength per second • Shorter wavelengths have higher frequencies • Longer wavelengths have lower frequencies

  42. Relationship between c, , and c =   = c /   = c /  - In visible, near IR, and thermal IR remote sensing, wavelength () is used to describe a system In microwave remote sensing, frequency () is often used to describe a system

  43. Stefan-Boltzman Law* • The total emitted radiation from a blackbody** (M) measured in Watts m-2is proportional to the fourth power of its absolute temperature (T) measured in Kelvin (K), and is calculated: M =  T4 where  is a constant (5.6697 x 10-8 W m-2 K-4) *Know this formula and be able to describe what it represents ** a blackbody is a theoretical construct that absorbs and radiates energy at the maximum possible rate per unit area at each wavelength for a given temperature.

  44. Planck’s formula** • Spectral emittance – S() S() = 2 h c2 / [5 (ech /  kT– 1)] Where h is Planck’s constant And k is the Stephan-Boltzman constant **you do NOT have to know this formula

  45. Planck’s formula gives basic shape of emittance curves Stephan Boltzman Law predicts how much total energy is emitted Note how total energy drops dramatically as temperature decreases

  46. Wien Displacement Law* • The wavelength with the highest level of emitted radiation (max) for an object of temperature T can be calculated as max = k / T where k = 2898 m ºK *know this formula and be able to describe what it represents

  47. Examples of Wien’s Displacement Law • T (sun) = 6000º K max = k / T = 2898/6000 = 0.483 m T (earth) = 300º K max = k / T = 2898/300 = 9.66 m

  48. Wein Displacement Law shows that as temperature increases, the wavelength of maximum emission decreases

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